Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session X09: Bio-mineralization, Hydration & Hardening in Colloidal Gels: Building Solid Materials out of Soft GelsInvited Live
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Sponsoring Units: DSOFT Chair: Niels Holton Andersen, MIT; Thibaut Divoux, MSE |
Friday, March 19, 2021 8:00AM - 8:36AM Live |
X09.00001: Hydrogel Mineralization via Amorphous Precursors Invited Speaker: Rosa Espinosa-Marzal Marine organisms exploit varied physical and chemical interactions between calcium carbonate and organic additives to yield mineral-organic complexes that are not only visually stunning but also highly functional. Despite recent leaps in the understanding of these systems, knowledge of the relation between kinetics of mineral growth, microstructure of the composite and mechanical response is still lacking. Our aim is to mechanistically elucidate potential pathways that afford control of the mineralization pathway of hydrogels and of their microstructure, and yield composites with tunable mechanical response. Our previous studies demonstrated that the formation of amorphous calcium carbonate precursors (ACC) throughout agarose hydrogels is a diffusion-limited process, and therefore, it is strongly affected by the solution composition and by the hydrogel composition. In contrast, amorphous precursors in the hydrogel control tightly the inclusion of the polymer into calcite, and crystal morphology, as well as the rate of crystal growth, affording a uniform crystal growth throughout the hydrogels, in the absence of concentration gradients, over a wide range of solution conditions and hydrogel compositions. Based on these findings, we have extended these studies to phosphates, and show that amorphous precursors also modulate the mineralization kinetics quite tightly. Furthermore, the phosphate-mineralized hydrogels exhibit key advantages with regard to microstructure -as provided by hydroxyapatite nanosheets- and mechanical response, compared to the mineralized hydrogels in the absence of phosphates. The results of this work not only reveal an important mechanism underlying (bio)mineralization but it can also inspire new avenues to craft biomimetic materials. |
Friday, March 19, 2021 8:36AM - 9:12AM Live |
X09.00002: Compositional and structural gradients in dental enamel: from nano- to microscale Invited Speaker: Derk Joester Dental enamel is a highly complex, hierarchically structured material. It is composed of hydroxylapatite crystallites, thousands of which are bundled into rods that are organized in a three-dimensional weave. This architecture provides great fracture resistance and a much-enhanced fatigue life. It has long been known that the susceptibility of enamel to caries, i.e. acid corrosion, is greatly dependent on the presence of magnesium, carbonate, and fluoride ions. However, imaging the distribution of these impurities in enamel or the organic/inorganic interface in the chiton tooth has remained challenging. UV-laser pulsed atom probe tomography (APT), in combination with correlative imaging and spectroscopy techniques, has given us remarkable new insights into nanoscale structure and composition that is integral to the mechanical properties of teeth and their resistance to corrosion.[1, 2, 3, 4] Here, I will report on the distribution of Mg2+, Na+, F-, and CO32- in the amorphous intergranular phase that cements together crystallites in human enamel. I will further describe highly characteristic gradients of these ions across individual crystallites and discuss implications of these gradients for the mechanical properties of enamel, its dissolution behavior, and enamel formation during tooth development. Finally, I will report on a new approach for mapping crystallite properties at the the length scale of individual enamel rods and the interrod enamel that separates them.[5] |
Friday, March 19, 2021 9:12AM - 9:48AM Live |
X09.00003: The physics of cement cohesion: from soft colloidal gels to hardened cement hydrates Invited Speaker: Emanuela Del Gado Cohesive forces develop in cement from the accumulation of multivalent ions in the water-based solution between the charged surfaces of cement hydrates and drive the setting of an initial soft colloidal gel into a progressively harder solid, a mineral glue that glues together concrete and determines its mechanics. I will discuss how the interlocking of ions and water in confinement determines the net nanoscale cohesion and links cement hydration chemistry to the emerging physical properties of the material. The resulting changes in the shape of the nanoscale forces determine the morphologies of the cement hydrate gels and ultimately the mechanics of the hardened material. I will analyze the role of spatial gradients in the development of the microstructure, similarities or differences with clay based materials and structural features that control durability and interactions with the environment of the hardened gels. Finally, I will discuss the implications for other hardening gels and for more sustainable construction materials. |
Friday, March 19, 2021 9:48AM - 10:24AM Live |
X09.00004: A quantitative approach to biomineralization and cement hydration, guided by (micro-)structural mechanics Invited Speaker: Christian Hellmich Relations between biological systems and man-made structures ahve been intimately related since the dawn of the latter, and recent decades have seen these efforts being extended more and more towards emerging systems "hardening" out of an originally liquid environment. |
Friday, March 19, 2021 10:24AM - 11:00AM Live |
X09.00005: Hierarchical porous materials: when 3D printing meets self-assembly Invited Speaker: Andre Studart Materials like bamboo, marine sponges and bone are remarkable examples of how living |
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